When I build all Plascore (no plywood) I like to build a male plug in the shape of the final boat with cheap AC construction plywood first. Then I put thin 4mil Visqueen over the form and cover it with Plascore.
Larry treats the Plascore like funny looking plywood and skips most of the male mold step. He fastens the Plascore to temporary rib-like formers and glasses that. Both methods work. Mine is more labor intensive but it is useful for trial and error boat design, when you are not working with an already established set of dimensions. Because, with the male mold you get to see what the shape is as you fiddle with its dimensions.
Me:
==> build the plug <==
==> Cover the plug with Plascore <==
Larry: Larry's page has a zillion images all on one page so it takes a long time to load. But there are a lot of good images there.
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http://mountaindogs.net/plascorebuild1 <==